1. Field of the Invention
The invention is related generally to the art of halftoning text. It finds particular application where gray, colored, scanned, or anti-aliased text is to be halftoned. The invention will, for the most part, be described in terms of italic and non-italic text. However, it is to be understood that the invention can be usefully applied to accommodate other text and text characteristics.
2. Description of Related Art
When text includes gray or unsaturated features, a halftone screen used in preparing the text for rendering can have a significant effect on a perceived print quality of the text. For example, most text fonts have predominant components in vertical and horizontal orientations. For instance this—t—consists predominantly of vertical and horizontal orientated components. Therefore, printing systems often use halftone screens with vertical and horizontal orientations to halftone text, such as using a high frequency vertical line screen. Typically, these halftone screens combine with the predominant components of most text fonts to produce interactions of an unobjectionably high frequency.
However, when text fonts or font modifications include predominant components in non-vertical or non-horizontal orientations, the vertical/horizontal nature of a typical text halftone screen can interact with those non-vertical/non-horizontal components to yield displeasing rendering artifacts. For example, the halftoning of many italic fonts or font modifications is known to be problematic. Italicized text is commonly slanted at a slope of about four to one (4/1, or about fourteen degrees from the vertical). The predominant components of italicized text combine with vertically oriented line or dot screens to produce text with edges that appear rough or jagged. FIG. 1 includes an exaggerated example of this phenomenon. In FIG. 1 a magnified 14 point, 50% gray level, italic letter “K” is rendered with a prior art, vertically oriented, line screen. Where the line screen interacts with a slanted edge or contour of the letter, the edge appears jagged.
The same or similar phenomena occur when halftoning certain portions of Roman (generally vertically and horizontally oriented) fonts. For example, the letters A, K, M, N, V, W, X, Y, and Z all contain diagonal features or components that are often rendered with a jagged appearance. Similarly, some curved portions of characters such as, S, P, B D, O, U, Q, G and C can interact poorly with the prior art vertical and horizontal oriented screening methods. The phenomenon generally leads to objectionable rendering results when text is gray, unsaturated color, anti-aliased, or possesses gray edges, for example, as a result of a scanning process.
For the forgoing reasons, there has been a desire to provide a text halftoning system that reduces or eliminates jaggedness in halftoned text.